Without limiting the scope of the invention, its background is described in connection with semiconductor devices, as an example.
Heretofore, in this field, the epitaxial growth of insulators on semiconductors has been an important step in the fabrication of various electronic devices, such as metal-insulator-semiconductor field effect transistors (MISFETs), silicon on insulator (SOI) technology, three dimensional integrated circuits, etc., as well as novel devices that cannot be achieved with amorphous insulators. Epitaxial growth of Group II fluoride on silicon has been studied extensively because of its technological and scientific interest. As one of the most promising candidates in this area, the CaF.sub.2 /Si couple has attracted considerable attention. From a materials preparation point of view, CaF.sub.2 is a relevant choice among the fluorides for deposition on silicon because it fits several important criteria for a good epitaxial system, i.e. small lattice mismatch and similar cubic structure. Previous studies have shown that the chemical and structural properties of the CaF.sub.2 /Si interface vary under different deposition conditions and that these variations can significantly change the electrical characteristics of a system incorporating this interface.
In the past, epitaxial CaF.sub.2 films have been grown by molecular beam epitaxy (MBE) with substrates held at a fixed temperature from 500.degree. C. to 800.degree. C. Many state-of-the-art characterization techniques, including high-resolution transmission electron microscopy (HRTEM), medium energy ion scattering (MEIS), x-ray photoemission spectroscopy (XPS) and x-ray standing wave (XSW), have been applied in the past to understand the interface structure between CaF.sub.2 and Si. The exact atomic model governing the initial stage of epitaxial growth is still widely disputed. In co-assigned patent application Ser. No. 07/704,535, a method is described that allows the growth of A-type films, i.e. the orientation of the CaF.sub.2 film is identical to the Si substrate.
One of the problems faced has been the poor interface quality between the CaF.sub.2 and Si surfaces, in particular, the presence of a high level of interface charge density.